Testing and modeling of a two-phase ejector

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Abstract

The ejector expansion refrigeration cycle is a modified vapor compression cycle in
which a two phase ejector is used to recover a portion of the work otherwise lost in the expansion
valve. The ejector improves cycle performance by increasing compressor inlet pressure and by
lowering the quality of the fluid entering the evaporator. Theoretically, a cooling COP
improvement of approximately 21 % is achievable for a typical refrigerating cycle and an ideal
ejector. If the ejector performed as well as typical single-phase ejectors, an improvement of 12%
could be achieved. Previous tests have demonstrated a smaller 3.7% improvement; the difference
is in the poor performance of the two-phase ejector.

The purpose of this research is to understand the operating characteristics of the two phase
ejector and to improve design. A two-phase ejector test rig has been constructed and
tested. Preliminary data show performance superior to previously tested two-phase ejectors, but
still inferior to single phase ejectors. Ejector performance corresponds to refrigeration cycle COP
improvements ranging from 3.9010 to 7.6%. This performance was obtained with an ejector
designed from single-phase ejector and wet steam ejector design methods. The poor performance
indicates the design methods must be improved for two-phase ejectors. This research has begun
the development of design methods for the two-phase ejectors and this research has developed
models to describe the fluid dynamics and thermodynamics of the ejector.